How does serum CK change over the course of muscular dystrophy progression?

• A. CK remains normal throughout disease progression
• B. CK levels rise steadily as disease progresses
• C. CK is typically very high early and may decrease as muscle mass is lost
• D. CK levels are irrelevant to dystrophy progression

Answer: (C)

The important idea is that CK in the blood tracks ongoing muscle membrane damage, not the total amount of muscle left. In muscular dystrophy, there’s rapid, ongoing muscle fiber breakdown early on, so many fibers leak CK into the bloodstream and levels become very high. As the disease progresses, a lot of muscle mass is lost and replaced by fat and fibrous tissue, leaving fewer muscle fibers that can leak CK. With less viable muscle to release CK, the serum CK can drop and may become normal or only mildly elevated, even though weakness and disability continue to worsen. So CK is typically very high early and may decrease as muscle mass is lost.